Question

Describe how the motility and secretions of the stomach contribute to the digestive process in a healthy human, making sure that you describe difference between the functional regions of the stomach.

in details, please

Answer 1

Describe how the motility and secretions of the stomach contribute to the digestive process in a healthy human, making sure that you describe difference between the functional regions of the stomach?

Ans.

Stomach, which is an essential part of the digestive system is a 'J' shaped organ located between the esophagus and small intestine. The main role of stomach is to partially digest the food particles and also regulates the rate at which they are released into small intestine. The stomach acts as a holding sac , holding about three to four litres of food and drink daily. The food is held for about two to six hours in stomach before being passed in to small intestine.The stomach wall has deep folds and the muscular wall of the stoamch churns the food and mixes it with gastric juices resulting in semi-liquid substance called chyme.

Based on structure and function stomach is divided into five parts namely, cardia, fundus, corpus, antrum and pylorus..

Cardia: The esophagus opens into the first part of the stomach called cardia. The food swallowed passes from esophagus to the first part of the stomach which is cardia. Gastric juices and acids that aid in digestion are produced in cardia.

Fundus: The upper, dome shaped region of the stomach that stores undigested food and gases that are released from chemical digestion.

Corpus: The main body of the stomach and is the largest of all the other parts, where the actual partial digestion process occurs is the cardia.

Pylorus: A funnel shaped structure of the stomach that opens into dueodenum of the small intestine is called pylorus. A thin circular band of smooth muscle called pyloric sphincter is located at the junction between pylorus of the stomach and duodenum of the small intestine. The pyloric sphincter acts as a valve regulating the flow of partially digested food from stomach to mall intestine.

The upper part of the stomach which includes cardia, fundus and corpus is called proximal stomach and the lower part of the stomach that includes antrum and pylorus is called distal stomach.

Motility and secretions of stomach in digestion:

The muscular wall of the stomach contributes the important functions of the stomach. The mucosa or the inner lining of stomach contains glands that produce acids and enzymes which aid in digestion. The inner lining f the stomach has a rough appearnce made by gastric folds which have gastric pits in them. The gastric pits contain gastric glands that secrete gastric juices which is a mucus fluid containing digestive enzymes and hydrochloric acid.

There are five types of secretory cells located in the gastric epithelial layer and they are as follows:

1. Surface mucous cells: These cells line the inner stomach and extend into the gastric pits and secrete an alkaline fluid containg mucin, which helps in protecting the stomach lining from exposure to acidity caused by gastric juices and enzymes.
2. Mucous neck cells: They are located deeper than surface mucous cells and secrete acid mucin which helps to maintain acidic conditions of the stomach.
3. Parietal cells: These cells produce intrinsic factor and hydrochloric acid (HCL). The main role of intrinsic factor is it protects vitamin B12 molecules from acidic conditons and aids in their trasnsport to small intestine. HCL is not directly secreted by the cells, The negative cholride ions and positive hydrogen ions are produced by the cells and they combine to form HCL. The low pH levels in the stoamch are maintained by HCL and also the enzymes that aid in digestion are activated by HCL. Hydrochloric acid also as a defence mechanism, protecting the stomach against foreign pathogens.
4. Cheif cells: They secrete pepsinogen and gastric lipase that aid in the breakdown of proteins and fats respectively.
5. G cells: They help in the secretion of gastrin into blood, which stimulates parietal cells and cheif cells to secrete HCL and pepsionogen respectively. Gastrin helps in contraction of esophagel spinchter, increases stomach motility and relaxes pyloric sphincter.

Summary:

The main functions of stomach are:

• It acts as a food reservoir, it stores food until it is moved into the small intestine.
• Partial digestion takes place in the stomach by the gastric juices relased inside th stomach. The bolus that enters the stomach is mixed up with gastric juices and is churned into smaller particles, resulting in chyme.
• Intrinsic factor which protects Vitamin B12 from acids is secreted in stomach.
• Stomach absorbs alcohol, short chain fatty acids and aspirin.
• It secretes gastrin, which is important for secretion of HCL.

Phases of gastric secretions:

The gastric juices secreted in the stomach help in digesting the food partially in the stomach. The gastric secreton happens in three phases and they are as follows:

• Cephalic phase:It is also called reflex phase, The secretion in this phase occurs much before the food enters the stomach. It occurs while eating the food. The smell, sight or taste of the food act as neurgenic signals causing cephalic phase of gastric secretion that originates in the cerebral cortex and apetite centres of hypothalamus and amygdala.
• Gastric phase: This phase of secretion occurs when the food actually reaches stomach. It occurs due to the neral and hormonal mechanisms that are triggered by the entry of food into stomach. Gastric secretions are stimulated in response to two factors, the amount of the chyme and chemical nature of the chyme. About 70% pf gastric secretion occurs in gastric phase.
• Intestinal phase: Gastric secretions are reduced in this phase in order to aid the transport of chyme to small intestine where further digestion takes place. The exit of chyme from stomach is a very slow and properly regulated process in order to prevent small intestine from being over loaded with chyme.